Method of stripping dyes from fibers



Patented Apr. 23, 1929.

EDWARD LESLIE HELWIG, OF BRISTOL TOWNSHIP, BUCKS COUNTY, PENNSYLVANIA, ASSIGNOR TO IROHM & HAAS COMPANY, A CORPORATION OF DELAWARE.

lHETT-IOD OF STRIPPING DYES FROM FIBERS.

No Drawing.

Hydrosulphites of the alkali-forming metals, principally sodium hydrosulphite, have been used for stripping dyes from fabrics. lVith these materials it is, however,

necessary to keep the bath alkaline, as other Wise'the material decomposes. I have discovered that if the stripping is carried on in a bath comprising zinc hydrosulphite and a hydrosulphite such as sodium hydrosulphite held in equilibrium by the presence of a soluble zinc salt and a soluble sodium salt, the use of an alkaline stabilizer is unnecessary, and it is even possible to maintain the bath slightly acid. The result is much more ellicient than when an alkaline solution is used and the injurious effect of alkalis on animal fibers can be avoided. The simplest way of obtaining a bath comprising the'equilibrium referred to is to dissolve together the soluble zine salt and the es) parently an equilibrium reaction is established according to the following formulas g In these formulas Me is intendedto represent a-monovalent alkali-forming metal and f Me" represents a similar bivalent metal.

The zinc hydrosulphite formed in these eqpilibriums is much more stable than the salts of 40 the alkaline or earth alkaline metals and serves as a stabilizer of the latter so that, the bath may even be broughtto the boiling point while on the acid side without decomposition setting in.

If a commercial powder is to be sold adapted for ready use 1n preparing a stripping bath, it is advantageousto use a partially anhydrous zinc salt in order to prevent a reaction startin in before the bath is prepared;

so For examp e, I may use zinc sulphate con-- as sodium hydrosulphite, though the- Application filed January 27, 1928. Serial No. 250,072.

taining approximately 12% of water of crystallization.

The following example illustrates my invention:

Picked wool shoddy was covered with water which was brought to a boil and there was then added 2 of the weight of the Wool in sodium hydrosulphite and a like Weight of zinc sulphate containing approximately 12% of water of crystallization. The boiling was continued until color had disappeared. The goods were then rinsed thoroughly and finished in the usual manner. The action was Very efficient and there was substantially no tendency for decomposition of the bath.

It is to be understood that the two salts may be added simultaneously in the form of a mixture, or they may be added separately, or they may be put first into solution. There is also awide latitude in regard to the temperature of the bath, the time of boiling and the percentages of materials used. important that the bath should not be mitted to become alkaline, is to be maintained.

This bath may be used on all commercial fibers such as those used in making fabrics and also on leather and other fibrous mate rials, which may be in the raw, intermediate or finished state.

What I claim is:

if its full eflicieney It is, however,

.1. The method of stripping dyes from fibers which comprises the steps of treating the fibers in a bath comprising zinc hydrosulphite and the hydrosulphite of an alkali orming metalin equilibrium with a soluble zinc salt and a saltof such alkali-forming metal.

2. The method of forming a bath for stripping dyes from fibers which comprises the step of dissolving together a hydrosulphite of an alkali-forming metal, and a soluble zinc salt.

\ 3. A new product adapted to form a stripping bath, 'amixture of a hydrosulphite of an alkali-forming metal and a soluble zinc salt having less of crystallization.

I EDWARD LESLIE HELWIG.

than the full amount of the water 

